The dataset contains records of Robber Crab (Birgus latro) mortality across Christmas Island, including location co-ordinates and details of sex and thoracic length. To manage the impact of road mortality on the species, this monitoring project is designed to assess spatial variation in road mortality. Basic data are collected at the site (sex, size, date, coordinates).
Credit
We at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
Purpose
The Australian territory of Christmas Island lies in the Indian Ocean, 2,600 km northwest of Perth and 500 km south of the Indonesian capital, Jakarta. Christmas Island National Park is 85 km2 in size and makes up almost two thirds of Christmas Island. The robber crab (Birgus latro) is categorized as Data Deficient on the IUCN Red List, and Christmas Island is thought to have one of the largest remaining populations. Robber crab road mortality appears to vary with changes in traffic density. Since the opening of the Christmas Island Immigration Detention Centre in late 2009, thousands of robber crabs have been run over on the island's roads in line with the increased population and vehicular traffic, especially at night. Park staff began marking the location of road kills using pink marker paint to denote the sites and make them visible in January 2010.
Lineage
1) Survey Design: Parks staff began painting the road kills on an ad hoc basis when it was noted there was a significant increase in mortality in a short period of time. Organised data recording began later in order to preserve the record and enable the production of maps and other outputs. Unfortunately, data collections have not always included a measure of effort, such as the roads driven, and how often, and as a result any significant statistical analysis of the occurrence of fatalities has been difficult to ascertain. It is hoped that records of vehicle registrations and staff numbers at detention centres since late 2009 may reveal significant correlations with road mortalities and provide a reportable and publishable result. Vehicle traffic recording equipment has also been incorporated into the program to provide greater data on vehicular movements.
2) Road Survey: Parks staff travel all the main roads on the island twice a week, early in the day. They record the roads travelled on and the date. When a dead robber crab is found, it is removed from the road, a circle with a cross in it is painted on the spot where the crab was killed, so the kill is only recorded once. The following details are recorded: the sex of the individual; the thoracic length to the nearest mm with callipers; the date and the UTM of the site. Sex is determined by the presence of egg claspers (like small hairy legs) on the abdomens of females, which are absent in males. In many records an animal's size and sex can not be determined due to damage caused by road traffic.
